It is unknown how blood rubies(BR) were created, but they are the currency used in Umu. A good rule of thumb: one BR equals to 100 US dollars, so to a lot of Flesh Realmers, these guys are incredibly stable financially. BR's can also be used in Black Markets to purchase different items, depending on the merchant, or be traded for another type of currency(i.e. trade 5 BR's for $500). Umuites usually come to Black Markets to trade their BR's for whatever currency their new home in Gaia will accept if they're wanting to start a new life or it's for the sake of a mission. However, if they want to go back to Umu, they can trade their money back for BR's, but there's always a high probability of them going back home with less BR's if they're not cautious with their budgeting.